Systems and methods for visualizing errors in video signals

ABSTRACT

Systems and methods for analyzing the performance of a digital network include capturing a stream of digital data, e.g., internet protocol (IP) packets, that represent streaming video, identifying which of the IP packets include bit errors, determining to which of a plurality of pixels the IP packets including bit errors belong and identifying such pixels as corrupted pixels, and illuminating only the corrupted pixels on a display of a tool. Corrupted pixels in different time blocks can be displayed with different colors to gain a better appreciation of the bit error rate over time.

BACKGROUND

1. Filed of the Invention

The present invention relates to telecommunications testing. Moreparticularly, the present invention relates to systems and methods forvisualizing bit errors occurring in telecommunication access networks.

2. Background

Today's widespread growth in deployment of higher speed DSL service,such as ADSU2/2+, enables telecom service providers to offer voice,video and data over a single twisted pair of copper wires. This is oftentermed the “triple play” of the telecommunications industry, and moreparticularly of the digital telecommunications industry.

For the successful adoption of triple play services, telecom providersmust meet or exceed the quality of service expected by customers.Quality of service can be impacted by many technical problems. Onecommon problem is the existence of faults in the copper pair that createfaults in the ADSL signal, which lead to lost packets and transmissiondelays. These lost packets and delays create slow data rates and degradethe quality of voice and video service.

The same concerns are also applicable to other telecom services, beyondADSL service, including ISDN service, and even service provided overfiber optic cable.

No matter what the physical network is composed of, telecom serviceproviders must routinely test and qualify their networks to ensure thequality of service that customers demand in the marketplace.

When analyzing a digital network, one common performance metric is themeasurement of bit error rate (BER). This metric is often measured bydevices known as bit error rate testers (BERTs), which are designedspecifically to test digital networks, systems and subsystems. Generallyspeaking, the rate of bits incorrectly conveyed over a network is ameasure of the bit error rate (BER) of that network, and is anindication of the performance and operability of the network. Typically,some sort of predetermined test pattern that is broken up into a streamof IP packets is sent through the network and a suitable BERT comparesthe received pattern with a stored version of the test pattern. The BERTitself may also be capable of generating the test pattern, sending thetest pattern out over the network, and receiving back the stream of datathat it has sent out.

One well-known BERT is the HST-3000 available from JDS Uniphase (SanJose, Calif.). This device is a handheld, modular platform for copperand multi-service testing. The device includes an LCD display that isoperable to display various menus and network performance data. As partof its functionality, the HST-3000 includes set-top-box (STB) emulationthat enables the HST-3000 to establish program streams in a terminatemode not requiring customer premises equipment (CPE). Quality of Service(QoS) parameter measurement along with detailed troubleshooting analysisfeatures make the HST-3000 a particularly advanced video tool.

Despite the availability of BERTs generally, and the relatively advancedHST-3000 in particular, there is nevertheless a need to further improveupon digital network analysis tools.

For example, testing video services delivered over various accessnetwork technologies (DSL, FTTx, etc.) present a complex environment toa field technician. While it is possible to analyze the quality of avideo transport stream by analyzing its corresponding digital data,there can be no subjective evaluation without decoding the “picture” forhuman evaluation. However, a decode process for a full motion videoprogram on a portable field test tool would be very expensive anddifficult to accomplish, especially on a typical small screen graphicaluser interface (GUI) display employed on a device like the HST-3000.Furthermore, “hide” algorithms in a typical video decoder hide variouserror conditions such as lost video data that would result in lostpixels on the television (monitor) screen.

Thus, there is a need for an improved portable digital video tester thatcan not only provide objective analysis of a video stream, but can alsoprovide a means for enabling a subjective analysis of the video.

SUMMARY OF THE INVENTION

The present invention provides, among other things, a subjectiveanalysis of the BER of a given bit stream and is particularly suitablefor a battery operated test tool, analyzers or bit error rate tester(BERT). Rather than decoding the full picture, which, in any event,would not necessarily reveal problematic video since conventionaldecoding schemes are specifically designed to hide impairments, thepresent invention may be configured to gain test access ahead of orbefore the decoder stage, and thus is able to analyze the raw data flowsuch that errors are more easily detected.

More specifically, embodiments of the present invention display on atest tool's graphical user interface (GUI) display only corrupted pixelsfrom a video stream flow. In addition, the present invention ispreferably able to capture these images from the screen and save them asa computer image file (e.g., JPEG, BITMAP, GIF, etc.) to a file systemfor later examination by the technician. Consequently, one can veryquickly, almost at a glance, “see” the errors showing up in the streamflow. Since test access is gained before any “hiding” of errors isaccomplished by a decoder, a true analysis of video errors can be made.The mechanism or methodology includes analyzing video streams in one orboth of two ways outlined below and obtaining data to be presented onthe display of the tester from either of the methodologies.

In a first implementation, compression schemes, such as MPEG-2 or MPEG-4or other compression schemes such as VC-1, are decoded and analyzed.Corrupted pixels are identified and then only those corrupted pixels arepresented on the display of the BERT for visual analysis. By onlyshowing corrupted pixels, the user can quickly determine the quality ofthe signal as opposed to a post decoded video stream which would atworst, show a full motion video with some pixels missing, and at best,show a corrected video stream, thus hiding the error.

In a second implementation, a test file stored in the BERT is used as areference and compared to the same test file sent over the network, andreceived for analysis by the test tool or BERT. In this case, thereceived data is compared to the stored data. Corrupted pixels areidentified and only the corrupted data presented on the display. Thetest file may be sent periodically over the network, or requested by thefield technician on demand.

In both cases, the decode function is preferably operated with thedecode “hide” algorithms turned off to show raw transport stream errors.With the hide algorithms turned off, raw network performance can be seenand analyzed.

Further, using a color display, a temporal component can be added to theanalysis by color coding the errors to show history in time blocks usingdifferent colors for each time block, as well as providing histogrampresentations of the data. On a gray scale display, the same effect canbe achieved for the error data. In addition, a simple quality errorscore (e.g., on a scale of 1 to 5) can be calculated from the error datato enable a subjective analysis to be scored in an objective manner. Thescoring parameters may be calculated in accordance with any well-knowntechnique.

These and other features of the present invention will be more fullyillustrated upon a reading of the following detailed description inconjunction with the associated drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary process for analyzing corrupted pixelsin accordance with an embodiment of the present invention.

FIGS. 2-4 depict exemplary screen displays corresponding to varyinglevels of detected bit error rate.

FIGS. 5-7 show test access points in different network types for a BERTin accordance with the present invention.

DETAILED DESCRIPTION

The present invention allows a field technician, using a portable,battery operated field tester to subjectively assess the BER of a givenbit stream. Because decoding and displaying an entire picture or videostream consumes significant amounts of power, the present invention ispreferably configured to gain test access ahead of or before the decoderstage, and is thus able to analyze the raw data flow such that errorsare more easily detected.

FIG. 1 shows an exemplary series of steps 100 for achieving thefunctionality of the present invention. As shown, the process begins atstep 110, and immediately moves to step 112 where an incoming datastream is captured. It is well-known in the art how to connect a biterror rate tester (BERT) or other field test device, such as the JDSUniphase's HST-3000, to a network. The data stream is preferably a videostream that is delivered over xDSL, FTTx (e.g., fiber to the “X”, suchas home) or ISDN, among others. The video format may be in accordancewith an MPEG-2, MPEG-4 or VC-1 format, among others. “Capturing” inaccordance with the present invention includes any one or a combinationof the following functions: storing, buffering, or creating image files(e.g., JPEGs) as the test is running, so the user can view the resultsat a later time.

Once the data stream is captured, corrupted packets, data, and, inparticular when dealing with video, corrupted pixels are identified atstep 114. There are several ways of identifying such packets, data orpixels. For instance, if insufficient information is available tocomplete a pixel, that pixel could be declared or identified as beingcorrupted. Since the invention is not CODEC specific, missing data canappear in several manners. Sometimes packets arrive out of order, aremissing, or are late and thus unusable. CRC checks, checksums, andFraming bits may be present in a particular video compression algorithm,and may be used to identify data that is corrupt or unusable when theinstant the invention receives the data.

In a preferred embodiment, metrics regarding the corrupted data areaccumulated at step 116 and numerical statistics can then be calculatedand displayed. Algorithms for such calculations are well-known to thosehaving skill in the art.

At step 118 and substantially simultaneously with step 116, only theidentified corrupted pixels are presented on the display (e.g., an LCDdisplay) of the BERT. The “corrupted” pixels are preferably displayed ina predetermined color in the location at which they would normally bedisplayed. In other words, as shown in FIGS. 2-4, the display of theBERT will include a “picture” of only the corrupted pixels. In this wayit is relatively simple for a field technician to glance at the displayand “see” subjectively, how bad (or good) a bit error rate is at a giventime. The display essentially highlights only the locations of pixelsthat are deemed corrupted.

FIG. 2 shows a display that shows a BER of about 0.1%. It can be seenthat the display includes relatively few places having lit-up corruptedpixels. FIG. 3 shows a BER of about 0.3%. More corrupted pixels areshown. FIG. 4 shows a display representing a BER of about 1% and thenumber of corrupted pixels is readily apparent.

Returning again to FIG. 1, after displaying the corrupted pixels on thedisplay, it is determined whether a temporal function is enabled. Ifnot, the process 100 simply ends at step 122. If the temporal functionis enabled, then at step 124 the BERT is configured, for the nextdisplay of corrupted pixels, to change the display color of thecorrupted pixels that will be presented. In this way, it is relativelysimple to compare on a time-based basis, how a BER might be changing.

From the foregoing, those skilled in the art will appreciate that basedon a quick view of the display screen of a BERT, one can “see” thenumber of errors showing up in a given stream of video data.Significantly, since test access is gained before any “hiding” of errorsis accomplished by a decoder, a true analysis of video errors can bemade. The present invention can be implemented in at least two ways.

In a first implementation, compression schemes, such as MPEG-2 or MPEG-4or other compression schemes such as VC-1, are decoded and analyzed.Corrupted pixels are identified and then only those corrupted pixels arepresented on the display of the BERT for visual analysis. In this case,the field technician might not be able to tell what kinds of pixelsmight be more susceptible to corruption since the technician might notnecessarily know what the streamed picture is supposed to look like inthe first place. Nevertheless, this implementation is useful as itprovides a real-world view of the network being analyzed.

In a second implementation, a test file stored in the BERT is used as areference and compared to the same test file sent over the network, andreceived for analysis by the test tool or BERT. In this case, thereceived data is compared to the stored data. Corrupted pixels areidentified and only the corrupted data presented on the display. Thetest file may be sent periodically over the network, or requested by thefield technician on demand. In this case, the technician, perhapsalready being familiar with what the test pattern normally looks like,can more quickly identify types of pixels that are tending to be moresusceptible to corruption.

Also, as mentioned above, if a color or gray scale display is available,a temporal component can be added to the analysis whereby color codingthe errors can be performed to show history in time blocks usingdifferent colors for each time block. In addition, histogram and likeviews can be generated and displayed for the user by relying on, forexample, results accumulated at step 116.

Furthermore, a simple quality error score (e.g., 1 to 5) can becalculated from the accumulated error data to enable a subjectiveanalysis to be scored in an objective manner. The scoring parameters maybe calculated in accordance with any well-known technique.

FIGS. 5-7 show test access points for a device operating in accordancewith the principles of the present invention for performing bit errortesting. FIG. 5 shows an xDSL implementation, FIG. 6 shows an ISDNimplementation, and FIG. 7 shows an FTTx implementation (in FIG. 7 OLTis an Optical Line Terminator, and ONT is an Optical Network Terminal.As shown, the BERT is connected to the given network downstream of aheadend, central office, or similar data stream source.

The foregoing disclosure of the preferred embodiments of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many variations andmodifications of the embodiments described herein will be apparent toone of ordinary skill in the art in light of the above disclosure. Thescope of the invention is to be defined only by the claims appendedhereto, and by their equivalents.

Further, in describing representative embodiments of the presentinvention, the specification may have presented the method and/orprocess of the present invention as a particular sequence of steps.However, to the extent that the method or process does not rely on theparticular order of steps set forth herein, the method or process shouldnot be limited to the particular sequence of steps described. As one ofordinary skill in the art would appreciate, other sequences of steps maybe possible. Therefore, the particular order of the steps set forth inthe specification should not be construed as limitations on the claims.In addition, the claims directed to the method and/or process of thepresent invention should not be limited to the performance of theirsteps in the order written, and one skilled in the art can readilyappreciate that the sequences may be varied and still remain within thespirit and scope of the present invention.

1. A method for analyzing a data stream representing video, comprising:capturing an incoming data stream representing video; identifyingcorrupted pixels represented by digital data in the data stream;displaying on a display only the corrupted pixels in locations on thedisplay at which respective corrupted pixels would otherwise be located;and, changing a color of the corrupted pixels to be displayed in asubsequent display of newly identified corrupted pixels.
 2. The methodof claim 1, further comprising accumulating data regarding the corruptedpixels.
 3. The method of claim 1, further comprising determining whethera temporal display function is enabled.
 4. The method of claim 1,wherein the method is performed by a portable bit error rate tester(BERT).
 5. The method of claim 4, wherein the BERT receives the datastream transmitted via a digital network.
 6. The method of claim 5,wherein the BERT identifies corrupted pixels by decoding the datastream.
 7. The method of claim 4, wherein the BERT stores apredetermined test pattern.
 8. The method of claim 7, wherein thepredetermined test pattern is transmitted via a digital network.
 9. Themethod of claim 1, wherein the data stream is transmitted via at leastone of Digital Subscriber line (xDSL), Integrated Services DigitalNetwork (ISDN) and Fiber to the X (FTTx).
 10. The method of claim 1,further comprising calculating a quality score of the data stream.
 11. Amethod of analyzing a performance of a digital network, comprising:capturing a stream of internet protocol (IP) packets that representstreaming video; identifying which of the IP packets include bit errors;determining to which of a plurality of pixels the IP packets includingbit errors belong and identifying such pixels as corrupted pixels; andilluminating only the corrupted pixels on a display; wherein the step ofilluminating only the corrupted pixels comprises illuminating thecorrupted pixels at a first moment in time with a first color andilluminating other corrupted pixels at a second moment in time with asecond color different from the first color.
 12. The method of claim 11,further comprising selecting whether to illuminate corrupted colors withdifferent colors.
 13. The method of claim 11, wherein the digitalnetwork comprises a Digital Subscriber line (xDSL) network.
 14. Themethod of claim 11, wherein the digital network comprises an IntegratedServices Digital Network (ISDN) network.
 15. The method of claim 11,further comprising comparing the streaming video to a predetermined testpattern.
 16. The method of claim 11, wherein the method is performed bya portable bit error rate tester (BERT).
 17. The method of claim 11,further comprising calculating a quality score of the streaming video.18. A portable, battery operated bit error rate tester, comprising: adisplay; means for capturing a stream of internet protocol (IP) packetsthat represent streaming video; means for identifying which of the IPpackets include bit errors; means for determining to which of aplurality of pixels the IP packets including bit errors belong andidentifying such pixels as corrupted pixels; and means for illuminatingonly the corrupted pixels on the display at a first moment in time witha first color and illuminating other corrupted pixels at a second momentin time with a second color different from the first color.